There are many applications in which a plurality of threaded connectors, usually arranged spaced from each other along a circle, have to be tightened or loosened. Such applications are for instance abutting flanges of pipes in a pipeline, which are connected by bolts extending through aligned bores in the flanges of the pipes, or covers of atomic reactors which have to be tightly connected by a plurality of bolts. Up to now such bolts have been individually tightened, which is of course quite a time-consuming task. It is pointed out that hydraulic wrenches are rather heavy and, depending on the force such wrench has to apply, such hydraulic wrenches may weight up to 200 pounds and such heavy wrenches have to be lifted and lowered by crane to apply such wrenches to successive threaded connectors to be tightened or loosened. The set-up time for moving the wrench from one to the next threaded connector to be tightened or loosened may therefore take from 5 minutes up to half an hour. While for some special applications apparatus have already been provided by means of which several bolts or threaded connectors could be tightened or loosened simultaneously, in such known apparatus a separate fluid-operated driving element has to be used for tightening or loosening each bolt or any other threaded connector, and such apparatus is extremely complicated, heavy and expensive, so that the handlng thereof is likewise difficult.
Another factor essential for the construction of hydraulic wrenches, respectively whether a hydraulic wrench of usual construction can be applied at all, especially a hydraulic wrench for simultaneously tightening or loosening two threaded connectors, is that the spacing of threaded connectors which have to be tightened or loosened varies considerably as well as the available overhead space for applying a hydraulic wrench of a usual construction. In many applications, the available overhead space is so small that hydraulic wrenches of known construction could not be used, and in such cases box wrenches have been used to which hammer blows have been applied to tighten or loosen a threaded connector. Of course, in such cases, a proper tightening of the threaded connectors with a predetermined force could never be obtained.